My invention relates to a discharge chute assembly for a moving hearth and, in particular, to an assembly for use with the rotary hearth of a calcining kiln.
As is known in the prior art, limestone, which is largely calcium carbonate, is reduced to lime or calcium oxide by subjecting the limestone to a high heat for a predetermined period of time. In one method of calcining, shown for example in U.S. Pat. No. 3,345,052, issued to H. L. Hall, the limestone is deposited in the form of small pellets on the surface of an annular hearth which is rotated continuously on a vertical axis to carry the pellets through successive heating zones of an annular kiln. When the pellets have been converted to lime and have moved to a certain point along the circular course, a belt or the like with vanes or pushers sweeps the pellets outwardly onto a stationary chute down which the lime slides into a hopper or the like.
One of the problems associated with hearth assemblies of the prior art relates to the transfer of the calcined pellets from the surface of the rotating hearth to the stationary chute. Because the hearth is composed of refractory materials and typically has a large diameter of ninety feet, for example, eccentricities develop along the outer periphery of the hearth, causing a periodic fluctuation in the displacement between the hearth periphery and the discharge chute. Imperfections in the circular tracks used to support the hearth may cause additional fluctuations in displacement. As a result, placing the chute sufficiently far from the hearth to provide adequate clearance results in substantial spillage of pellets in the gap between the hearth and the discharge chute, wasting material and possibly interfering with the mechanical operation of the hearth. Discharge chutes of the prior art also have the problem of "hanging up" of the pellets along the length of the chute.